Demonstration of Law of Segregation

Description
Heredity, or the inheritance of parental character, in offsprings has long been the subject of a great deal of experimental work in biology. Gregor Mendel, an Austin monk, carried out an extensive series of experiments on the common edible pea (Pisum sativum) to find out their inheritance patterns. The law of segregation is one of the laws proposed by Mendel, which states that the genes or alleles present in F1 will not blend or contaminate or influence one another; rather, they segregate in the same pure form that they arrived from the parent. The members of an allele pair separate from each other without influencing each other, when an individual forms haploid germ cells.

To understand the pattern of inheritance of the vestigial wing mutation of Drosophila melanogaster, we must understand the law of segregation.

Materials

• Drosophila melanogaster
• Vestigial-winged mutant of Drosophila melanogaster
• Bottles with standard medium
• Anaesthetic ether
• Etherizer
  
• Re-etherizer
• Needles
• Brushes
• Yeast granules
• Glass plate

Procedure
Drosophila melanogaster normal- and vestigial-winged mutant flies were cultured in standard media bottles separately. When pupae in the cultured bottles were ready, the bottles were cleaned by taking out all the flies present there. The enclosed male and female virgins were isolated, aged for 2–3 days and then, by mating these virgins, crosses were made. They were crossed in the following way to get the F1 generation:

• Normal female X vestigial-winged virgin male
• Normal female X vestigial male

The progeny produced in the F1 generation were observed for the phenotypic expression and the data were proposed. Then F1 males and females were inbred and the resulting F2 phenotypes were observed and the data were recorded.

Observation
Parents: phenotype normal female X ebony males
F1 progeny: phenotype all normal-colored flies.
Inbreed: F1 females X F1 males.
F2 progeny: phenotype normal flies and ebony flies.
Phenotypic ratio: 163: 52
Phenotype Observed Expected Deviation d2 d2/E = X2
Normal females
And males 163 161.25 1.75 3.06 0.189
Ebony females
And males 52 53.75 – 1.75 3.06 0.056
Sx2 = 0.075
Degree of freedom = 2 – 1 = 1

Analysis of Results
At the 5% level of significance and at 1 degree of freedom, the table value is 3.85.
In direct crosses, the calculated value of x2 = 0.075, which is less than the table value.
In reciprocal crosses, the calculated x2 value is less than the table value.
In both the crosses, the deviation was not significant, so the null hypothesis is accepted.

Reciprocal Cross
PARENTS: phenotype ebony female X normal male
F1: all normal-body colored flies
Inbreed: F1 female × F1 male
F2: normal flies and ebony flies
Phenotypic ratio: 180:48

Phenotype Observed Expected Deviation d2 d2/E
Normal male
And female 180 171 9 81 0.47
Ebony male and
Female 46 57 9 81 1.42
Sx2 = 189
Degree of freedom = 2 – 1 = 1.